1,375 research outputs found
The end-to-end testbed of the Optical Metrology System on-board LISA Pathfinder
LISA Pathfinder is a technology demonstration mission for the Laser
Interferometer Space Antenna (LISA). The main experiment on-board LISA
Pathfinder is the so-called LISA Technology Package (LTP) which has the aim to
measure the differential acceleration between two free-falling test masses with
an accuracy of 3x10^(-14) ms^(-2)/sqrt[Hz] between 1 mHz and 30 mHz. This
measurement is performed interferometrically by the Optical Metrology System
(OMS) on-board LISA Pathfinder. In this paper we present the development of an
experimental end-to-end testbed of the entire OMS. It includes the
interferometer and its sub-units, the interferometer back-end which is a
phasemeter and the processing of the phasemeter output data. Furthermore,
3-axes piezo actuated mirrors are used instead of the free-falling test masses
for the characterisation of the dynamic behaviour of the system and some parts
of the Drag-free and Attitude Control System (DFACS) which controls the test
masses and the satellite. The end-to-end testbed includes all parts of the LTP
that can reasonably be tested on earth without free-falling test masses. At its
present status it consists mainly of breadboard components. Some of those have
already been replaced by Engineering Models of the LTP experiment. In the next
steps, further Engineering Models and Flight Models will also be inserted in
this testbed and tested against well characterised breadboard components. The
presented testbed is an important reference for the unit tests and can also be
used for validation of the on-board experiment during the mission
Eigenmode in a misaligned triangular optical cavity
We derive relationships between various types of small misalignments on a
triangular Fabry-Perot cavity and associated geometrical eigenmode changes. We
focus on the changes of beam spot positions on cavity mirrors, the beam waist
position, and its angle. A comparison of analytical and numerical results shows
excellent agreement. The results are applicable to any triangular cavity close
to an isosceles triangle, with the lengths of two sides much bigger than the
other, consisting of a curved mirror and two flat mirrors yielding a waist
equally separated from the two flat mirrors. This cavity shape is most commonly
used in laser interferometry. The analysis presented here can easily be
extended to more generic cavity shapes. The geometrical analysis not only
serves as a method of checking a simulation result, but also gives an intuitive
and handy tool to visualize the eigenmode of a misaligned triangular cavity.Comment: 17 pages, 21 figure
Spontaneous Breaking of Translational Invariance in One-Dimensional Stationary States on a Ring
We consider a model in which positive and negative particles diffuse in an
asymmetric, CP-invariant way on a ring. The positive particles hop clockwise,
the negative counterclockwise and oppositely-charged adjacent particles may
swap positions. Monte-Carlo simulations and analytic calculations suggest that
the model has three phases; a "pure" phase in which one has three pinned blocks
of only positive, negative particles and vacancies, and in which translational
invariance is spontaneously broken, a "mixed" phase with a non-vanishing
current in which the three blocks are positive, negative and neutral, and a
disordered phase without blocks.Comment: 7 pages, LaTeX, needs epsf.st
Components for the LISA local interferometry
This article describes some preliminary results on essential components for the LISA interferometry, namely photodiode preamplifiers and voltage references
Comparative analysis of 2D and 3D models of turbulent natural convection and thermal surface radiation in closed areas
Turbulent natural convection with surface thermal radiation in air-filled enclosures has been investigated. The equations of conservation of mass, momentum and energy are solved using both finite difference and control volume methods. It should be noted that the working medium is Newtonian and heat conducting fluid, where the Boussinesq approximation is valid. The walls are supposed to be gray, diffuse emitters and reflectors of radiation. The left and right surfaces of the enclosure are isothermal walls, while other surfaces are adiabatic walls. The considered fluid flow is turbulent. The main aim of the present research is to compare the heat transfer process in 2D and 3D enclosures. Detailed results including flow profiles, temperature fields, and average Nusselt numbers have been presented
Thermal diagnostic of the Optical Window on board LISA Pathfinder
Vacuum conditions inside the LTP Gravitational Reference Sensor must comply
with rather demanding requirements. The Optical Window (OW) is an interface
which seals the vacuum enclosure and, at the same time, lets the laser beam go
through for interferometric Metrology with the test masses. The OW is a
plane-parallel plate clamped in a Titanium flange, and is considerably
sensitive to thermal and stress fluctuations. It is critical for the required
precision measurements, hence its temperature will be carefully monitored in
flight. This paper reports on the results of a series of OW characterisation
laboratory runs, intended to study its response to selected thermal signals, as
well as their fit to numerical models, and the meaning of the latter. We find
that a single pole ARMA transfer function provides a consistent approximation
to the OW response to thermal excitations, and derive a relationship with the
physical processes taking place in the OW. We also show how system noise
reduction can be accomplished by means of that transfer function.Comment: 20 pages, 14 figures; accepted for publication in Class. Quantum Gra
Stochastic Models on a Ring and Quadratic Algebras. The Three Species Diffusion Problem
The stationary state of a stochastic process on a ring can be expressed using
traces of monomials of an associative algebra defined by quadratic relations.
If one considers only exclusion processes one can restrict the type of algebras
and obtain recurrence relations for the traces. This is possible only if the
rates satisfy certain compatibility conditions. These conditions are derived
and the recurrence relations solved giving representations of the algebras.Comment: 12 pages, LaTeX, Sec. 3 extended, submitted to J.Phys.
Transport properties of chemically synthesized polypyrrole thin films
The electronic transport in polypyrrole thin films synthesized chemically
from the vapor phase is studied as a function of temperature as well as of
electric and magnetic fields. We find distinct differences in comparison to the
behavior of both polypyrrole films prepared by electrochemical growth as well
as of the bulk films obtained from conventional chemical synthesis. For small
electric fields F, a transition from Efros-Shklovskii variable range hopping to
Arrhenius activated transport is observed at 30 K. High electric fields induce
short range hopping. The characteristic hopping distance is found to be
proportional to F^(-1/2). The magnetoresistance R(B) is independent of F below
a critical magnetic field, above which F counteracts the magnetic field induced
localization.Comment: 6 pages, 5 figure
Conformal mechanics inspired by extremal black holes in d=4
A canonical transformation which relates the model of a massive relativistic
particle moving near the horizon of an extremal black hole in four dimensions
and the conventional conformal mechanics is constructed in two different ways.
The first approach makes use of the action-angle variables in the angular
sector. The second scheme relies upon integrability of the system in the sense
of Liouville.Comment: V2: presentation improved, new material and references added; the
version to appear in JHE
Aperture Increase Options for the Dutch Open Telescope
This paper is an invitation to the international community to participate in
the usage and a substantial upgrade of the Dutch Open Telescope on La Palma
(DOT, \url{http://dot.astro.uu.nl}).
We first give a brief overview of the approach, design, and current science
capabilities of the DOT.
The DOT database (\url{http://dotdb.phys.uu.nl/DOT}) now contains many
tomographic image sequences with 0.2-0.3 arcsec resolution and up to multi-hour
duration. You are welcome to pull them over for analysis.
The main part of this contribution outlines DOT upgrade designs implementing
larger aperture. The motivation for aperture increase is the recognition that
optical solar physics needs the substantially larger telescope apertures that
became useful with the advent of adaptive optics and viable through the DOT's
open principle, both for photospheric polarimetry at high resolution and high
sensitivity and for chromospheric fine-structure diagnosis at high cadence and
full spectral sampling.
Realization of an upgrade requires external partnership(s). This report about
DOT upgrade options therefore serves also as initial documentation for
potential partners.Comment: in press,"Physics of Chromospheric Plasmas" (Coimbra), ASP 368, 573
(2007
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